class Dog(): 
    """一次模拟小狗的简单尝试"""
    def __init__(self, name, age): 
        """初始化属性name和age"""
        self.name = name 
        self.age = age

    def sit(self): 
        """模拟小狗被命令时蹲下""" 
        print(self.name.title()+ " is now sitting.")

    def roll_over(self): 
        """模拟小狗被命令时打滚""" 
        print(self.name.title()+ " rolled over!")


my_dog = Dog('blue', '6')
print("My dog's name is " + my_dog.name.title() + ".") 
print("My dog is " + str(my_dog.age) + " years old.")
my_dog.sit()
my_dog.roll_over()